Characterising the loading direction sensitivity of 3D woven composites: Effect of z-binder architecture

Three different architectures of 3D carbon fibre woven composites (orthogonal, ORT; layer-to-layer, LTL; angle interlock, AI) were tested in quasi-static uniaxial tension. Mechanical tests (tensile in on-axis of warp and weft directions as well as 45° off-axis) were carried out with the aim to study the loading direction sensitivity of these 3D woven composites. The z-binder architecture (the through-thickness reinforcement) has an effect on void content, directional fibre volume fraction, mechanical properties (on-axis and off-axis), failure mechanisms, energy absorption and fibre rotation angle in off-axis tested specimens. Out of all the examined architectures, 3D orthogonal woven composites (ORT) demonstrated a superior behaviour, especially when they were tested in 45° off-axis direction, indicated by high strain to failure (∼23%) and high translaminar energy absorption (∼40 MJ/m³). The z-binder yarns in ORT architecture suppress the localised damage and allow larger fibre rotation during the fibre “scissoring motion” that enables further strain to be sustained by the in-plane fabric layers during off-axis loading.     

The influence of lateral forces on the cell stiffness measurement by optical tweezers vertical indentation

We studied the lateral forces arising during the vertical indentation of the cell membrane by an optically trapped microbead, using back focal plane interferometry to determine force components in all directions. We analyzed the cell-microbead interaction and showed that indeed the force had also lateral components. Using the Hertz model, we calculated and compared the elastic moduli resulting from the total and vertical forces, showing that the differences are important and the total force should be considered. To confirm our results we analyzed cells from two breast cancer cell lines: MDA-MB-231 and HBL-100, known to have different cancer aggressiveness and hence stiffness.     

Measuring the human body's microclimate using a thermal manikin

The human body is surrounded by a microclimate, which results from its convective release of heat. In this study, the air temperature and flow velocity of this microclimate were measured in a climate chamber at various room temperatures, using a thermal manikin simulating the heat release of the human being. Different techniques (Particle Streak Tracking, thermography, anemometry, and thermistors) were used for measurement and visualization. The manikin surface temperature was adjusted to the particular indoor climate based on simulations with a thermoregulation model (UCBerkeley Thermal Comfort Model). We found that generally, the microclimate is thinner at the lower part of the torso, but expands going up. At the head, there is a relatively thick thermal layer, which results in an ascending plume above the head. However, the microclimate shape strongly depends not only on the body segment, but also on boundary conditions: The higher the temperature difference between the surface temperature of the manikin and the air temperature, the faster the airflow in the microclimate. Finally, convective heat transfer coefficients strongly increase with falling room temperature, while radiative heat transfer coefficients decrease. The type of body segment strongly influences the convective heat transfer coefficient, while only minimally influencing the radiative heat transfer coefficient.     

Effects of compressive stresses on torsional fatigue

Rolling contact fatigue (RCF) is the dominant failure mode in properly installed and maintained ball and roller element bearings. Lundberg and Palmgren in their seminal publication indicated that this failure is due to the alternating component of shear stress. Thus, torsional fatigue experiments have been used to predict the RCF behavior of bearing materials. In non-conformal contacts, due to Hertzian pressure the contact experiences large compressive stresses. Hence, it is critical to take into account the effect of these large compressive stresses in torsional fatigue to better simulate RCF conditions. This paper presents an investigation of torsional fatigue of bearing steels, while the effects of combined compressive stress and its relevance to material behavior in rolling contact fatigue is examined. An MTS test rig was used to investigate the fatigue life of several bearing steels and their failure mechanisms were evaluated through fractography. Then the effects of compressive stresses on torsional fatigue were investigated. A set of custom designed clamp fixtures were designed, developed and used to apply Hertzian pressures of up to 2.5 GPa on the torsion specimens. The experimental results indicate that at high cycle fatigue, a combination of shear and biaxial compression, by application of Hertzian contact, is more detrimental to fatigue life than shear alone; however, as expected it has little to negligible effects in the low cycle fatigue regime. Also the failure mode changes such that fracture planes form a cup and cone pair with multiple internal cracks as opposed to helical planes observed in pure torsion which are formed by a single crack. A 3D finite element model (using ABAQUS) was developed to investigate the fatigue damage accumulation, crack initiation, and propagation in the material. The topology of steel microstructure is modeled employing a randomly generated Voronoi tessellation wherein each Voronoi cell represents a material grain and the boundaries between the cells are assumed to represent the weak plane in the steel matrix. Continuum damage mechanics (CDM) was used to model material degradation during the fatigue process. A comprehensive damage evolution equation is developed to account for the effect of mean stress on fatigue. The model predicts the fatigue lives and crack patterns successfully both in presence and absence of compressive stresses.     

Performance of supercritical carbon dioxide sprays as coolants and lubricants in representative metalworking operations

This paper investigates the cooling and lubrication properties of supercritical carbon dioxide (scCO₂) sprays as potential substitutes for aqueous emulsions and straight oils used in the metalworking industry today. Sprays of rapidly expanding scCO₂ act to cool and lubricate machining and forming processes by delivering a mixture of dry ice and lubricant deep into the cutting/forming zone. In this work, experiments with turning, milling, drilling, thread cutting, and thread forming were performed with scCO₂ and other metalworking fluids (MWFs) to evaluate their relative performance with respect to tool wear and machining torque. Observations reveal that scCO₂–MWFs are more effective in removing heat from the tool-workpiece interface than conventionally delivered (flood) aqueous MWFs as well as other gas-based MWF sprays. In addition, scCO₂–MWFs delivered in lubricant-expanded phase, where scCO₂ is used to increase volume of lubricant in the spray field, are shown to provide better lubricity than straight oils and oil-in-air minimum quantity lubrication (MQL) sprays. As a result, scCO₂–MWFs can reduce tool wear and improve machining productivity in a wide range of manufacturing operations leading to appreciable improvements in the economics of manufacturing. Also given that CO₂ is a recovered waste gas that is non-toxic, scCO₂–MWFs can improve the environmental and worker health performance of manufacturing operations.     

Supercritical CO2 fractionation of omega-3 lipids from fish by-products: Plant and process design,modeling, economic feasibility

Biopharmaceutical, nutraceutical and food sectors are experiencing an increasing market interest in omega-3 concentrates. Fish and fish processing by-products represent the major source of lipids rich in omega-3. The present work focuses on the supercritical CO₂ fractionation of fish oil derivatives for obtaining omega-3 concentrates, which seems a promising process given that it allows utilizing low temperatures (well below 100 °C) and it can be performed also at industrial scale. The process was conceived, modeled, and evaluated in terms of the main parameters affecting its performances: solvent to feed ratio, reflux ratio, temperature, and pressure of both the fractionation column and the column head separator.The process was further optimized minimizing its operating costs. The optimum foresaw operating the column at high temperature (80 °C) and pressure (19.5 MPa), which allowed for a reduced reflux ratio (=0.92) and solvent to feed ratio (=63). At these conditions, the process cost per unit product (omega-3 concentrate) turned out to be of about 2.3 €/kg.Finally, the plant was designed for three different throughputs: 10, 100, and 300 kg/h. This allowed estimating the investment costs, in order to outline a preliminary process feasibility evaluation.     

Molecular dynamics simulation of gas-phase ozone reactions with sabinene and benzene

Gas-phase reactions of ozone (O₃) with volatile organic compounds were investigated both by experiment and molecular simulations. From our experiments, it was found ozone readily reacts with VOC pure components and reduces it effectively. By introducing ozone intermittently, the reaction between VOC and ozone is markedly enhanced. In order to understand the relationship between intermediate reactions and end products, ozone reaction with benzene and alicyclic monoterpene sabinene were simulated via a novel hybrid quantum mechanical/molecular mechanics (QM/MM) algorithm that forced repeated bimolecular collisions. Molecular orbital (MO) rearrangements (manifested as bond dissociation or formation), resulting from the collisions, were computed by semi-empirical unrestricted Hartree-Fock methods (e.g., RM1). A minimum of 975 collisions between ozone and targeted organic species were performed to generate a distribution of reaction products. Results indicated that benzene and sabinene reacted with ozone to produce a range of stable products and intermediates, including carbocations, ring-scission products, as well as peroxy (HO₂ and HO₃) and hydroxyl (OH) radicals. Among the stable sabinene products observed included formaldehyde and sabina-ketone, which have been experimentally demonstrated in gas-phase ozonation reactions. Among the benzene ozonation products detected composed of oxygen mono-substituted aromatic C₆H₅O, which may undergo further transformation or rearrangement to phenol, benzene oxide or 2,4-cyclohexadienone; a phenomenon which has been experimentally observed in vapor-phase photocatalytic ozonation reactions.     

Fundamental investigation on nano-precision surface finishing of electroless Ni–P-plated STAVAX steel using magnetic compound fluid slurry

Electroless nickel–phosphorus (Ni–P) plating used in a range of hot embossing metal molds/dies and injection metal molds/dies must be manufactured to nano-precision roughness for proper operation of the molds/dies. We therefore developed a novel polishing technique for mirror surface finishing of this kind of magnetic material using a magnetic compound fluid (MCF) slurry. The effects of the magnetic and gravitational forces acting on the carbonyl iron particles (CIPs) and abrasive particles (APs) within the MCF slurry were studied first, and the behaviors of the CIPs and APs in the presence of an external magnetic field were predicted. Then, experiments were performed to confirm the predictions by investigating the distribution of the CIPs and APs on the working surface of the MCF slurry. Finally, four MCF slurries containing CIPs and APs with different diameters were employed to finish the Ni–P-plated STAVAX steel specimen at different working gaps. The results revealed that for the magnetic workpiece, the resultant vertical force attracted CIPs towards the work surface, whereas APs were pushed away from the work surface. However, the CIPs and APs showed opposite behaviors with the non-magnetic workpiece. The percentage of APs distributed on the working surface increased and the distribution became more even as either the diameter of the CIPs or the working gap increased, whereas that of CIPs had the opposite tendency. The MCF slurry containing bigger CIPs and smaller APs should be employed and the working gap should be set at a smaller value in order to perform mirror surface finishing of a magnetic Ni–P-plated surface. Under the experimental conditions in this work, the Ni–P-plated surface quality improved significantly, and a mirror surface roughness (Ra) of 4 nm was successfully achieved without leaving scratches or particle adhesion when using an MCF slurry containing CIPs 7 μm in diameter and APs 1 μm in diameter, showing that MCF slurries containing commercial CIPs are applicable to the nano-precision finishing of magnetic materials.     

On the experimental and numerical investigation of clay/epoxy nanocomposites

Due to increasing use of clay/epoxy nanocomposites in industry, investigation of mechanical properties of clay nanocomposites has become of great interest. While the stiffening mechanism of clay nanocomposites is well documented, there is still not a clear understanding about how addition of clays affect the fracture behavior of clay/epoxy nanocomposites. The main aim of this paper is to measure and explain the effect of clays on ductility reduction of these nanocomposites. First, epoxy and clay/epoxy nanocomposites with different clay weight ratio were built. Then, the damage parameters of epoxy and clay/epoxy nanocomposites were measured by variation of the elasticity modulus. Based on loading–unloading experiments, the Lemaitre damage parameters for epoxy and clay/epoxy nanocomposites were extracted. Crack initiation and propagation in dog-bone sample were simulated for epoxy and clay/epoxy nanocomposites using the eXtended Finite Element Method (XFEM). The comparison between experimental and numerical results shows that the proposed method can predict the crack initiation location and propagation path in clay/epoxy nanocomposites.     

Bubble Volume and Aspect Ratio Generated in Non‐Newtonian Fluids

Bubble formation from an orifice submerged in quiescent polyacrylamide aqueous solution was investigated numerically with a sharp‐interface coupled level‐set/volume‐of‐fluid method based on the rheological characteristics of the fluid. In both non‐Newtonian fluids and Newtonian fluids, the numerical approach was able to capture accurately the deformation of the bubble surface, validated by comparison with experimental results. The effects of orifice diameter, solution mass concentration, and gas flow rate on bubble volume and aspect ratio were evaluated. Both the instantaneous and detached volume decrease with the orifice diameter but increase with mass concentration and gas flow rate. The aspect ratio at the departing point tends to rise with the orifice diameter and mass concentration and falls with the gas flow rate.